1. Field of the Invention
This invention relates to pipe couplings, more particularly dielectric pipe couplings used in high temperature, corrosive environments.
2. Brief Description of the Prior Art
For many years the oil, sulfur and gas industries have been faced with the problem of combating corrosion in their underground wells and associated surface piping caused by the hot, corrosive fluids encountered in normal well operation. Exposure of the steel pipes, tube and casings to these fluids obviously decreases the lifespan and increases the maintenance costs associated with the wells. In cases where a well exhibits marginal production, the increases maintenance costs could determine whether or not the well is kept in production.
A typical proposed solution to minimize the effects of corrosion is to coat the interior of the pipe and to cement the outside into the well formation. Obviously, this solution is imperfect since it prohibits removal of the pipe for remedial work on the well. Another solution is to use stainless steel or other corrosive resistant material for the piping. In many cases, however, this solution is economically impossible due to the much higher costs of such materials.
A more viable solution to the problem is to use the corrosive resistant material, such as stainless steel only through the most corrosive area of the well operation and to join it to a string of mild steel piping used to make up the remainder of the system. However, the corrosive fluids (acid or basic) form an ideal environment for galvanic corrosion between the dissimilar metals. This results in a faster corrosive attack of the mild steel piping and a slower attack of the stainless steel as compared with the same materials when they are not in contact.
Several attempts have been made in the past to eliminate or minimize the galvanic action between dissimilar piping materials. U.S. Pat. Nos. 2,950,928; 3,185,501 and 3,346,274 all show electrically insulating joints for connecting pipes or tubes together. All of these connecting joints utilize at least one resilient insulating member to prevent physical contact between the pipes. This would render it impractical to use them in the high temperature, corrosive environment of a sulfur, oil or gas well due to the rapid deterioration of the resilient element. Also, the inferior pull-out strength of these joints would prohibit their use in a well string or similar piping arrangement. Other insulating pipe couplings are shown in U.S. Pat. Nos. 1,165,114 and 3,871,687. However, neither of these couplings are designed for use in the high-temperature, corrosive environment of an oil, sulfur or gas well.